Synchronization channel design for new carrier type

ABSTRACT

Certain aspects of the present disclosure relate to synchronization channel design for a new carrier type. In certain aspects, a User Equipment (UE) may first search for legacy locations of PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal), and attach to a cell that transmits the legacy PSS/SSS. Then the UE may be provided with information indicating a search space for PSS and SSS of a new carrier. The UE may then search for the PSS and SSS for the new carrier based on the received information. The relative spacings in time between the PSS and SSS for the first carrier may be different from the relative spacings in time between the PSS and SSS for the second carrier. In alternative aspects, the UE may receive a frequency offset value and determine PSS/SSS locations for the new carrier based on the frequency offset value and spaced center frequencies.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

The present Application for Patent is a divisional of patent applicationSer. No. 3/836,711, entitled “SYNCHRONIZATION CHANNEL DESIGN FOR NEWCARRIER TYPE,” filed on Mar. 15, 2013, which claims priority to U.S.Provisional Application No. 61/613,428, entitled “SYNCHRONIZATIONCHANNEL DESIGN FOR NEW CARRIER TYPE,” filed Mar. 20, 2012, each of whichis assigned to the assignee hereof and hereby expressly incorporated byreference herein.

FIELD

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more specifically, to synchronization channel designfor new carrier type.

BACKGROUND

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. Examples of such multiple-access networks include CodeDivision Multiple Access (CDMA) networks, Time Division Multiple Access(TDMA) networks, Frequency Division Multiple Access (FDMA) networks,Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA)networks.

A wireless communication network may include a number of base stationsthat can support communication for a number of user equipments (UEs). AUE may communicate with a base station via the downlink and uplink. Thedownlink (or forward link) refers to the communication link from thebase station to the UE, and the uplink (or reverse link) refers to thecommunication link from the UE to the base station.

SUMMARY

Certain aspects of the present disclosure provide a method for wirelesscommunications by a user equipment (UE). The method generally includesdetecting a primary synchronization signal (PSS) and secondarysynchronization signal (SSS) for a first carrier, receiving informationindicating a search space for a PSS and SSS of a second carrier, andsearching for the PSS and SSS of the second carrier based on thereceived information, wherein relative spacings in time between the PSSand SSS for the first carrier are different from the relative spacingsin time between the PSS and SSS for the second carrier.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (UE). The apparatusgenerally includes means for detecting a primary synchronization signal(PSS) and secondary synchronization signal (SSS) for a first carrier,means for receiving information indicating a search space for a PSS andSSS of a second carrier, and means for searching for the PSS and SSS ofthe second carrier based on the received information, wherein relativespacings in time between the PSS and SSS for the first carrier aredifferent from the relative spacings in time between the PSS and SSS forthe second carrier.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (UE). The apparatusgenerally includes at least one processor and a memory coupled to the atleast one processor. The at least one processor is generally configuredto detect a primary synchronization signal (PSS) and secondarysynchronization signal (SSS) for a first carrier, receive informationindicating a search space for a PSS and SSS of a second carrier, andsearch for the PSS and SSS of the second carrier based on the receivedinformation, wherein relative spacings in time between the PSS and SSSfor the first carrier are different from the relative spacings in timebetween the PSS and SSS for the second carrier.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications by a user equipment (UE). Thecomputer program product generally includes a computer-readable mediumcomprising code for detecting a primary synchronization signal (PSS) andsecondary synchronization signal (SSS) for a first carrier, receivinginformation indicating a search space for a PSS and SSS of a secondcarrier, and searching for the PSS and SSS of the second carrier basedon the received information, wherein relative spacings in time betweenthe PSS and SSS for the first carrier are different from the relativespacings in time between the PSS and SSS for the second carrier.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a base station (BS). The method generally includestransmitting a primary synchronization signal (PSS) and secondarysynchronization signal (SSS) for a first carrier, transmittinginformation indicating, to a user equipment (UE), a search space for aPSS and SSS of a second carrier, and transmitting the PSS and SSS of thesecond carrier based on the transmitted information, wherein relativespacings in time between the PSS and SSS for the first carrier aredifferent from the relative spacings in time between the PSS and SSS forthe second carrier.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (BS). The apparatusgenerally includes means for transmitting a primary synchronizationsignal (PSS) and secondary synchronization signal (SSS) for a firstcarrier, means for transmitting information indicating, to a userequipment (UE), a search space for a PSS and SSS of a second carrier,and means for transmitting the PSS and SSS of the second carrier basedon the transmitted information, wherein relative spacings in timebetween the PSS and SSS for the first carrier are different from therelative spacings in time between the PSS and SSS for the secondcarrier.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (BS). The apparatusgenerally includes at least one processor and a memory coupled to the atleast one processor. The at least one processor is generally configuredto transmit a primary synchronization signal (PSS) and secondarysynchronization signal (SSS) for a first carrier, transmit informationindicating, to a user equipment (UE), a search space for a PSS and SSSof a second carrier, and transmit the PSS and SSS of the second carrierbased on the transmitted information, wherein relative spacings in timebetween the PSS and SSS for the first carrier are different from therelative spacings in time between the PSS and SSS for the secondcarrier.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications by a user equipment (BS). Thecomputer program product generally includes a computer-readable mediumcomprising code for transmitting a primary synchronization signal (PSS)and secondary synchronization signal (SSS) for a first carrier,transmitting information indicating, to a user equipment (UE), a searchspace for a PSS and SSS of a second carrier, and transmitting the PSSand SSS of the second carrier based on the transmitted information,wherein relative spacings in time between the PSS and SSS for the firstcarrier are different from the relative spacings in time between the PSSand SSS for the second carrier.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a user equipment (UE). The method generally includesdetermining a frequency offset value, determining locations fordetecting a primary synchronization signal (PSS) and secondarysynchronization signal (SSS) for a carrier based on the frequency offsetvalue and spaced center frequencies, and searching for the PSS and SSSof the carrier at the determined locations.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (UE). The apparatusgenerally includes means for determining a frequency offset value, meansfor determining locations for detecting a primary synchronization signal(PSS) and secondary synchronization signal (SSS) for a carrier based onthe frequency offset value and spaced center frequencies, and means forsearching for the PSS and SSS of the carrier at the determinedlocations.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (UE). The apparatusgenerally includes at least one processor and a memory coupled to the atleast one processor. The at least one processor is generally configuredto determine a frequency offset value, determine locations for detectinga primary synchronization signal (PSS) and secondary synchronizationsignal (SSS) for a carrier based on the frequency offset value andspaced center frequencies, and search for the PSS and SSS of the carrierat the determined locations.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications by a user equipment (UE). Thecomputer program product generally includes a computer-readable mediumcomprising code for determining a frequency offset value, determininglocations for detecting a primary synchronization signal (PSS) andsecondary synchronization signal (SSS) for a carrier based on thefrequency offset value and spaced center frequencies, and searching forthe PSS and SSS of the carrier at the determined locations.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a base station (BS). The method generally includesdetermining a frequency offset value, determining locations fortransmitting a primary synchronization signal (PSS) and secondarysynchronization signal (SSS) for a carrier, for detection by a userequipment (UE), based on the frequency offset value and spaced centerfrequencies, and transmitting the PSS and SSS of the carrier at one ofthe determined locations.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (BS). The apparatusgenerally includes means for determining a frequency offset value, meansfor determining locations for transmitting a primary synchronizationsignal (PSS) and secondary synchronization signal (SSS) for a carrier,for detection by a user equipment (UE), based on the frequency offsetvalue and spaced center frequencies, and means for transmitting the PSSand SSS of the carrier at one of the determined locations.

Certain aspects of the present disclosure provide an apparatus forwireless communications by a user equipment (BS). The apparatusgenerally includes at least one processor and a memory coupled to the atleast one processor. The at least one processor is generally configuredto determine a frequency offset value, determine locations fortransmitting a primary synchronization signal (PSS) and secondarysynchronization signal (SSS) for a carrier, for detection by a userequipment (UE), based on the frequency offset value and spaced centerfrequencies, and transmit the PSS and SSS of the carrier at one of thedetermined locations.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications by a user equipment (BS). Thecomputer program product generally includes a computer-readable mediumcomprising code for determining a frequency offset value, determininglocations for transmitting a primary synchronization signal (PSS) andsecondary synchronization signal (SSS) for a carrier, for detection by auser equipment (UE), based on the frequency offset value and spacedcenter frequencies, and transmitting the PSS and SSS of the carrier atone of the determined locations.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of awireless communications network in accordance with certain aspects ofthe present disclosure.

FIG. 2 is a block diagram conceptually illustrating an example of aframe structure in a wireless communications network in accordance withcertain aspects of the present disclosure.

FIG. 2A shows an example format for the uplink in Long Term Evolution(LTE) in accordance with certain aspects of the present disclosure.

FIG. 3 shows a block diagram conceptually illustrating an example of aNode B in communication with a user equipment device (UE) in a wirelesscommunications network in accordance with certain aspects of the presentdisclosure.

FIG. 4 illustrates an example heterogeneous network having legacy andnon-legacy UEs in accordance with certain aspects of the presentdisclosure.

FIG. 5 illustrates an example Primary Synchronization Signal (PSS)sequence and alternating Secondary Synchronization Signal (SSS)sequences with a periodicity of 5 ms, in accordance with certain aspectsof the present disclosure.

FIG. 6 illustrates example operations, performed by a user equipment(UE), for detecting PSS/SSS of a new carrier type in accordance withcertain aspects of the present disclosure.

FIG. 6A illustrates example components capable of performing theoperations illustrated in FIG. 6, in accordance with certain aspects ofthe present disclosure.

FIG. 7 illustrates example operations, performed by a base station (BS),for transmitting PSS/SSS of a new carrier type in accordance withcertain aspects of the present disclosure.

FIG. 8 illustrates example operations, performed by a UE, for detectingPSS/SSS of a new carrier type in accordance with certain aspects of thepresent disclosure.

FIG. 8A illustrates example components capable of performing theoperations illustrated in FIG. 8, in accordance with certain aspects ofthe present disclosure

FIG. 9 illustrates example operations, performed by a base station (BS),for transmitting PSS/SSS of a new carrier type in accordance withcertain aspects of the present disclosure.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part ofUniversal Mobile Telecommunication System (UMTS). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS thatuse E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the wireless networks andradio technologies mentioned above as well as other wireless networksand radio technologies. For clarity, certain aspects of the techniquesare described below for LTE, and LTE terminology is used in much of thedescription below.

Example Wireless Network

FIG. 1 shows a wireless communication network 100, which may be an LTEnetwork. The wireless network 100 may include a number of evolved NodeBs (eNBs) 110 and other network entities. An eNB may be a station thatcommunicates with user equipment devices (UEs) and may also be referredto as a base station, a Node B, an access point, etc. Each eNB 110 mayprovide communication coverage for a particular geographic area. Theterm “cell” can refer to a coverage area of an eNB and/or an eNBsubsystem serving this coverage area, depending on the context in whichthe term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a Closed Subscriber Group (CSG), UEs for users in the home,etc.). An eNB for a macro cell may be referred to as a macro eNB. An eNBfor a pico cell may be referred to as a pico eNB. An eNB for a femtocell may be referred to as a femto eNB or a home eNB. In the exampleshown in FIG. 1, eNBs 110 a, 110 b, and 110 c may be macro eNBs formacro cells 102 a, 102 b, and 102 c, respectively. eNB 110 x may be apico eNB for a pico cell 102 x. eNBs 110 y and 110 z may be femto eNBsfor femto cells 102 y and 102 z, respectively. An eNB may support one ormultiple (e.g., three) cells.

The wireless network 100 may also include relay stations. A relaystation is a station that receives a transmission of data and/or otherinformation from an upstream station (e.g., an eNB or a UE) and sends atransmission of the data and/or other information to a downstreamstation (e.g., a UE or an eNB). A relay station may also be a UE thatrelays transmissions for other UEs. In the example shown in FIG. 1, arelay station 110 r may communicate with eNB 110 a and a UE 120 r inorder to facilitate communication between eNB 110 a and UE 120 r. Arelay station may also be referred to as a relay eNB, a relay, etc.

The wireless network 100 may be a heterogeneous network that includeseNBs of different types, e.g., macro eNBs, pico eNBs, femto eNBs,relays, etc. These different types of eNBs may have different transmitpower levels, different coverage areas, and different impact oninterference in the wireless network 100. For example, macro eNBs mayhave a high transmit power level (e.g., 20 watts) whereas pico eNBs,femto eNBs, and relays may have a lower transmit power level (e.g., 1watt).

The wireless network 100 may support synchronous or asynchronousoperation. For synchronous operation, the eNBs may have similar frametiming, and transmissions from different eNBs may be approximatelyaligned in time. For asynchronous operation, the eNBs may have differentframe timing, and transmissions from different eNBs may not be alignedin time. The techniques described herein may be used for bothsynchronous and asynchronous operation.

A network controller 130 may couple to a set of eNBs and providecoordination and control for these eNBs. The network controller 130 maycommunicate with the eNBs 110 via a backhaul. The eNBs 110 may alsocommunicate with one another, e.g., directly or indirectly via wirelessor wireline backhaul.

The UEs 120 may be dispersed throughout the wireless network 100, andeach UE may be stationary or mobile. A UE may also be referred to as aterminal, a mobile station, a subscriber unit, a station, etc. A UE maybe a cellular phone, a personal digital assistant (PDA), a wirelessmodem, a wireless communication device, a handheld device, a laptopcomputer, a cordless phone, a wireless local loop (WLL) station, atablet, etc. A UE may be able to communicate with macro eNBs, pico eNBs,femto eNBs, relays, etc. In FIG. 1, a solid line with double arrowsindicates desired transmissions between a UE and a serving eNB, which isan eNB designated to serve the UE on the downlink and/or uplink. Adashed line with double arrows indicates interfering transmissionsbetween a UE and an eNB.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition the system bandwidth into multiple(K) orthogonal subcarriers, which are also commonly referred to astones, bins, etc. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (K) may bedependent on the system bandwidth. For example, K may be equal to 128,256, 512, 1024, or 2048 for system bandwidth of 1.4, 3, 5, 10, or 20megahertz (MHz), respectively. The system bandwidth may also bepartitioned into subbands. For example, a subband may cover 1.08 MHz,and there may be 1, 2, 4, 8, or 16 subbands for system bandwidth of 1.4,3, 5, 10, or 20 MHz, respectively.

FIG. 2 shows a frame structure used in LTE. The transmission timelinefor the downlink may be partitioned into units of radio frames. Eachradio frame may have a predetermined duration (e.g., 10 milliseconds(ms)) and may be partitioned into 10 subframes with indices of 0 through9. Each subframe may include two slots. Each radio frame may thusinclude 20 slots with indices of 0 through 19. Each slot may include Lsymbol periods, e.g., L=7 symbol periods for a normal cyclic prefix (asshown in FIG. 2) or L=6 symbol periods for an extended cyclic prefix.The 2L symbol periods in each subframe may be assigned indices of 0through 2L-1. The available time frequency resources may be partitionedinto resource blocks. Each resource block may cover N subcarriers (e.g.,12 subcarriers) in one slot.

In LTE, an eNB may send a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) for each cell in the eNB. Theprimary and secondary synchronization signals may be sent in symbolperiods 6 and 5, respectively, in each of subframes 0 and 5 of eachradio frame with the normal cyclic prefix (CP), as shown in FIG. 2. Thesynchronization signals may be used by UEs for cell detection andacquisition. The eNB may send a Physical Broadcast Channel (PBCH) insymbol periods 0 to 3 in slot 1 of subframe 0. The PBCH may carrycertain system information.

The eNB may send a Physical Control Format Indicator Channel (PCFICH) inthe first symbol period of each subframe, as shown in FIG. 2. The PCFICHmay convey the number of symbol periods (M) used for control channels,where M may be equal to 1, 2 or 3 and may change from subframe tosubframe. M may also be equal to 4 for a small system bandwidth, e.g.,with less than 10 resource blocks. The eNB may send a Physical HARQIndicator Channel (PHICH) and a Physical Downlink Control Channel(PDCCH) in the first M symbol periods of each subframe (not shown inFIG. 2). The PHICH may carry information to support hybrid automaticrepeat request (HARQ). The PDCCH may carry information on resourceallocation for UEs and control information for downlink channels. TheeNB may send a Physical Downlink Shared Channel (PDSCH) in the remainingsymbol periods of each subframe. The PDSCH may carry data for UEsscheduled for data transmission on the downlink.

The eNB may send the PSS, SSS, and PBCH in the center 1.08 MHz of thesystem bandwidth used by the eNB. The eNB may send the PCFICH and PHICHacross the entire system bandwidth in each symbol period in which thesechannels are sent. The eNB may send the PDCCH to groups of UEs incertain portions of the system bandwidth. The eNB may send the PDSCH tospecific UEs in specific portions of the system bandwidth. The eNB maysend the PSS, SSS, PBCH, PCFICH, and PHICH in a broadcast manner to allUEs, may send the PDCCH in a unicast manner to specific UEs, and mayalso send the PDSCH in a unicast manner to specific UEs.

A number of resource elements may be available in each symbol period.Each resource element (RE) may cover one subcarrier in one symbol periodand may be used to send one modulation symbol, which may be a real orcomplex value. Resource elements not used for a reference signal in eachsymbol period may be arranged into resource element groups (REGs). EachREG may include four resource elements in one symbol period. The PCFICHmay occupy four REGs, which may be spaced approximately equally acrossfrequency, in symbol period 0. The PHICH may occupy three REGs, whichmay be spread across frequency, in one or more configurable symbolperiods. For example, the three REGs for the PHICH may all belong insymbol period 0 or may be spread in symbol periods 0, 1, and 2. ThePDCCH may occupy 9, 18, 32, or 64 REGs, which may be selected from theavailable REGs, in the first M symbol periods. Only certain combinationsof REGs may be allowed for the PDCCH.

A UE may know the specific REGs used for the PHICH and the PCFICH. TheUE may search different combinations of REGs for the PDCCH. The numberof combinations to search is typically less than the number of allowedcombinations for the PDCCH. An eNB may send the PDCCH to the UE in anyof the combinations that the UE will search.

FIG. 2A shows an exemplary format 200A for the uplink in LTE. Theavailable resource blocks for the uplink may be partitioned into a datasection and a control section. The control section may be formed at thetwo edges of the system bandwidth and may have a configurable size. Theresource blocks in the control section may be assigned to UEs fortransmission of control information. The data section may include allresource blocks not included in the control section. The design in FIG.2A results in the data section including contiguous subcarriers, whichmay allow a single UE to be assigned all of the contiguous subcarriersin the data section.

A UE may be assigned resource blocks in the control section to transmitcontrol information to an eNB. The UE may also be assigned resourceblocks in the data section to transmit data to the Node B. The UE maytransmit control information in a Physical Uplink Control Channel(PUCCH) 210 a, 210 b on the assigned resource blocks in the controlsection. The UE may transmit data or both data and control informationin a Physical Uplink Shared Channel (PUSCH) 220 a, 220 b on the assignedresource blocks in the data section. An uplink transmission may spanboth slots of a subframe and may hop across frequency as shown in FIG.2A.

A UE may be within the coverage of multiple eNBs. One of these eNBs maybe selected to serve the UE. The serving eNB may be selected based onvarious criteria such as received power, path loss, signal-to-noiseratio (SNR), etc.

A UE may operate in a dominant interference scenario in which the UE mayobserve high interference from one or more interfering eNBs. A dominantinterference scenario may occur due to restricted association. Forexample, in FIG. 1, UE 120 y may be close to femto eNB 110 y and mayhave high received power for eNB 110 y. However, UE 120 y may not beable to access femto eNB 110 y due to restricted association and maythen connect to macro eNB 110 c with lower received power (as shown inFIG. 1) or to femto eNB 110 z also with lower received power (not shownin FIG. 1). UE 120 y may then observe high interference from femto eNB110 y on the downlink and may also cause high interference to eNB 110 yon the uplink.

A dominant interference scenario may also occur due to range extension,which is a scenario in which a UE connects to an eNB with lower pathloss and lower SNR among all eNBs detected by the UE. For example, inFIG. 1, UE 120 x may detect macro eNB 110 b and pico eNB 110 x and mayhave lower received power for eNB 110 x than eNB 110 b. Nevertheless, itmay be desirable for UE 120 x to connect to pico eNB 110 x if the pathloss for eNB 110 x is lower than the path loss for macro eNB 110 b. Thismay result in less interference to the wireless network for a given datarate for UE 120 x.

In an aspect, communication in a dominant interference scenario may besupported by having different eNBs operate on different frequency bands.A frequency band is a range of frequencies that may be used forcommunication and may be given by (i) a center frequency and a bandwidthor (ii) a lower frequency and an upper frequency. A frequency band mayalso be referred to as a band, a frequency channel, etc. The frequencybands for different eNBs may be selected such that a UE can communicatewith a weaker eNB in a dominant interference scenario while allowing astrong eNB to communicate with its UEs. An eNB may be classified as a“weak” eNB or a “strong” eNB based on the relative received power ofsignals from the eNB received at a UE (and not based on the transmitpower level of the eNB).

FIG. 3 shows a block diagram of a design of a base station or an eNB 110and a UE 120, which may be one of the base stations/eNBs and one of theUEs in FIG. 1. For a restricted association scenario, the eNB 110 may bemacro eNB 110 c in FIG. 1, and UE 120 may be UE 120 y. The eNB 110 mayalso be a base station of some other type. The eNB 110 may be equippedwith T antennas 334 a through 334 t, and the UE 120 may be equipped withR antennas 352 a through 352 r, where in general T≥1 and R≥1.

At the eNB 110, a transmit processor 320 may receive data from a datasource 312 and control information from a controller/processor 340. Thecontrol information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. Thedata may be for the PDSCH, etc. The transmit processor 320 may process(e.g., encode and symbol map) the data and control information to obtaindata symbols and control symbols, respectively. The transmit processor320 may also generate reference symbols, e.g., for the PSS, SSS, andcell-specific reference signal. A transmit (TX) multiple-inputmultiple-output (MIMO) processor 330 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, and/or thereference symbols, if applicable, and may provide T output symbolstreams to T modulators (MODs) 332 a through 332 t. Each modulator 332may process a respective output symbol stream (e.g., for OFDM, etc.) toobtain an output sample stream. Each modulator 332 may further process(e.g., convert to analog, amplify, filter, and upconvert) the outputsample stream to obtain a downlink signal. T downlink signals frommodulators 332 a through 332 t may be transmitted via T antennas 334 athrough 334 t, respectively.

At the UE 120, antennas 352 a through 352 r may receive the downlinksignals from the eNB 110 and may provide received signals todemodulators (DEMODs) 354 a through 354 r, respectively. Eachdemodulator 354 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator 354 may further process the input samples (e.g., for OFDM,etc.) to obtain received symbols. A MIMO detector 356 may obtainreceived symbols from all R demodulators 354 a through 354 r, performMIMO detection on the received symbols, if applicable, and providedetected symbols. A receive processor 358 may process (e.g., demodulate,deinterleave, and decode) the detected symbols, provide decoded data forthe UE 120 to a data sink 360, and provide decoded control informationto a controller/processor 380.

On the uplink, at the UE 120, a transmit processor 364 may receive andprocess data (e.g., for the PUSCH) from a data source 362 and controlinformation (e.g., for the PUCCH) from the controller/processor 380. Thetransmit processor 364 may also generate reference symbols for areference signal. The symbols from the transmit processor 364 may beprecoded by a TX MIMO processor 366 if applicable, further processed bymodulators 354 a through 354 r (e.g., for SC-FDM, etc.), and transmittedto the eNB 110. At the eNB 110, the uplink signals from the UE 120 maybe received by antennas 334, processed by demodulators 332, detected bya MIMO detector 336 if applicable, and further processed by a receiveprocessor 338 to obtain decoded data and control information sent by theUE 120. The receive processor 338 may provide the decoded data to a datasink 339 and the decoded control information to the controller/processor340.

The controllers/processors 340, 380 may direct the operation at the eNB110 and the UE 120, respectively. The controller/processor 380 and/orother processors and modules at the UE 120 may perform or directoperations for blocks 600 and 800 in FIGS. 6 and 8, and/or otherprocesses for the techniques described herein. The memories 342 and 382may store data and program codes for base station 110 and UE 120,respectively. A scheduler 344 may schedule UEs for data transmission onthe downlink and/or uplink.

FIG. 4 illustrates an example heterogeneous network having legacy andnon-legacy UEs in accordance with certain aspects of the presentdisclosure. In certain aspects non-legacy UEs (e.g. Rel 11 macro UE 120y) may support a new carrier type that is not supported by legacy UEs(e.g. Rel 8/9/10 macro UE 120 u). Macro cell 110 c may transmit PSS/SSS.In LTE Rel-8/9/10, the time locations of PSS/SSS relative to each otherfor FDD and TDD are designed to be different, in order to facilitateearly detection of the frame structure type (FDD or TDD) by the legacyUEs. However, any change of the time locations of PSS/SSS, differentfrom the current Rel-8/9/10 locations, may result in one additional pairof PSS/SSS relative locations—one for FDD and the other for TDD. As aresult, if new time locations of PSS/SSS are introduced for the newcarrier type, a Rel-11 UE (e.g. non-legacy macro UE 120 y) may need tohandle four possible sets of PSS/SSS relative locations. This isdiscussed in more detail below.

In LTE, cell identities range from 0 to 503. Synchronization signals aretransmitted in the center 62 resource elements (REs) around the DC toneto help detect cells. The synchronization signals comprise two parts: aPrimary Synchronization Signal (PSS) and a Secondary SynchronizationSignal (SSS).

FIG. 5 illustrates an example PSS sequence 502 and alternating SSSsequences 504 ₀, 504 ₁ with a periodicity of 5 ms, in accordance withcertain aspects of the present disclosure. The PSS allows a UE to obtainframe timing modulo 5 ms and part of the physical layer cell identifier(cell ID), and specifically cell id modulo 3. Three different PSSsequences exist with each sequence mapping to a disjoint group of 168cell IDs. Based on Zadoff-Chu (ZC) sequences, the PSS sequence is chosenfrom one of 3 sequences based on a PSS Index=Cell ID modulo 3. The samesequence is transmitted every 5 ms as shown in FIG. 5.

The SSS is used by the UE to detect the LTE frame timing modulo 10 msand to obtain the cell ID. The SSS is transmitted twice in each 10 msradio frame as depicted in FIG. 5. The SSS sequences are based onmaximum length sequences, known as M-sequences, and each SSS sequence isconstructed by interleaving, in the frequency-domain, two length-31Binary Phase Shift Keying (BPSK)-modulated sequences. These two codesare two different cyclic shifts of a single length-31 M-sequence. Thecyclic shift indices of the M-sequences are derived from a function ofthe physical layer cell identity group. The two codes are alternatedbetween the first and second SSS transmissions in each radio frame.

In other words, two sequences for a cell ID that alternate every 5 msare transmitted. The SSS sequence is obtained by first choosing from aset of 168 different sequences (different sets for subframes 0 and 5)based on an SSS Index (=floor(Cell ID/3)) and then scrambling the chosensequence using a sequence which is a function of the PSS Index. Hence,while searching for the SSS, if the PSS Index is known, a UE may onlyneed to search up to 168 sequences.

Spacing between the PSS and the SSS helps a UE to distinguish betweenExtended Cyclic Prefix (CP) and Normal CP modes and between TDD (TimeDivision Duplex) and FDD (Frequency Division Duplex) modes.

A typical searching operation may involve first locating the PSSsequences transmitted by neighboring eNBs (i.e., determining the timingand the PSS index), followed by SSS detection for the found PSS Indexaround the determined timing.

Both PSS and SSS detection may involve using samples over multiplebursts to improve the chances of detection and reduce false detectionrates. Using multiple bursts provides time diversity. Spacing the burstsfar apart improves the time diversity, but increases the time taken fordetection.

Example Synchronization Channel Design for New Carrier Type in LTE-A

In certain aspects, system performance may be improved by introducing atleast one new carrier type, NCT (e.g., in the context of carrieraggregation) in standards releases (e.g. LTE Rel-11). Discussed hereinare certain aspects related to PSS/SSS design for the new carrier type.In certain aspects, the new carrier type provides additional resources(e.g. time/frequency resources) for communication between a base station(BS) and a user equipment (UE).

In certain aspects, by default, a same PSS/SSS design as earlierreleases (e.g., Rel. 8) may be maintained for the new carrier type,including the sequence design and the time-frequency location of thePSS/SSS. However, legacy UEs (e.g., Rel-8 UE) that do not support thenew carrier type may unnecessarily waste resources (e.g., time andpower) to acquire the PSS and SSS of the new carrier type only to bebarred from further camping on the new carrier type later. This may leadto wastage of UE resources.

As used herein, the term “legacy” generally refers to devices,structures, designs, or the like that are compatible with an earlierversion of a standard and is a relative term. For example, “legacy” mayrefer to Rel 8/9/10 while Rel 11 or later may be referred to as“non-legacy.”

Thus, in certain aspects, there may be a benefit in legacy UEs findingout quickly that a frequency belongs to the new carrier type, or makingthe NCT invisible to legacy UEs.

One way to make the NCT invisible to legacy UEs is to use a new PSS/SSSdesign for the NCT different from the legacy PSS/SSS design. In anaspect, the non-backward compatible new PSS/SSS design may make the newcarrier invisible to the legacy UEs, and consequently, save the legacyUEs from spending resources on any subsequent procedures after PSS/SSSacquisition (and before being barred from further camping on the newcarrier type at a later stage). However, in certain aspects, it may notbe easy to re-design a new set of PSS/SSS sequences for the new carriertype, since it may involve a lot of standardization and implementationefforts. Thus, in certain aspects, the same Rel-8 PSS/SSS sequences maybe used by the new carrier type at least for non-synchronization newcarriers.

Currently (e.g. in Rel-8/9/10), the frequency location of PSS/SSS makesit possible for the UE to acquire PSS/SSS prior to knowledge aboutsystem bandwidth. In an aspect, such property of the current systems maybe retained in cases where the new carrier type is used.

In LTE Rel-8/9/10, the time locations of PSS/SSS relative to each otherfor frequency division duplex (FDD) and time division duplex (TDD) aredesigned to be different, in order to facilitate early detection of theframe structure type (FDD or TDD). In certain aspects, in addition tothe legacy FDD and TDD positions, additional relative positions for PSSand SSS may be defined to differentiate between FDD and TDD of the newcarrier type. Any change of the time locations of PSS/SSS, differentfrom the current Rel-8/9/10 locations, may result in one additional pairof PSS/SSS relative locations—one for FDD and the other for TDD.

As a result, if new time locations of PSS/SSS are introduced for the newcarrier type, even if a legacy UE detects the PSS of the new carriertype, if may not detect the corresponding SSS due to the new relativepositions of the PSS-SSS defined for the new carrier type, and may giveup relatively quickly. However, a non-legacy UE may need to handle fourpossible sets of PSS/SSS relative locations. The new time locations alsoneed to consider the location of physical broadcast channel (PBCH), andpotentially, the symbols containing demodulation reference signal(DM-RS). This means more time and power consumption.

In certain aspects, a non-legacy UE may first (e.g., by default) searchfor the legacy PSS/SSS locations and attach to a cell that transmits thelegacy PSS/SSS. Then the UE may be provided with a channel list thatexplicitly identifies the channels on which the UE may perform searchfor the PSS/SSS signals of a new carrier, assuming only the newlocations and not the legacy locations. Thus, it may not be necessaryfor a non-legacy UE to search for four possible sets of PSS/SSS relativelocations. For example, the UE may first detect the PSS/SSS at legacylocations, and then receive information indicating a search space forthe PSS/SSS for the new carrier type. The UE may then search for thePSS/SSS of the new carrier based on the received information. In anaspect, this technique may be used only if the new carrier type is in acarrier aggregation configuration with a legacy carrier type.

In certain aspects, the received information may include two bits, onebit for indicating new carrier type, and the second bit for indicatingFDD or TDD mode. Alternatively, the second bit may be implicitlyincluded in the band number or channel number of the carrier. In anaspect, the information may include at least one bit to indicate that acarrier belongs to a new carrier type. In certain aspects, a relativespacing in time between PSS and SSS may be the same regardless ofwhether the second bit indicates FDD or TDD mode. In someimplementations, the received information may be included in a MasterInformation Block (MIB) carried on the PBCH channel or a SystemInformation Block (SIB) carried on the PDSCH channel. In an aspect, theinformation may be provided to the UE in a neighbour list, including aunicast or broadcast neighbour list. After identifying the PSS/SSS ofthe new carrier, the UE may register with the new carrier and utilizethe additional bandwidth of the new carrier in aggregation with thelegacy carrier.

According to certain aspects, the information transmitted to the UE maycomprise at least one bit indicating the cyclic prefix type of thesecond carrier.

According to certain aspects, a relative spacing in time between PSS andSSS may be different depending on whether a frequency division duplexing(FDD) mode or a time division duplexing (TDD) mode is used.

FIG. 6 illustrates example operations 600, performed by a UE, fordetecting PSS/SSS of a new carrier type in accordance with certainaspects of the present disclosure.

Operations 600 may begin, at 602 by detecting a PSS and an SSS for afirst carrier. At 604, information may be received indicating a searchspace for a PSS and SSS of a second carrier. At 606, the PSS and SSS ofthe second carrier may be searched, based on the received information.In an aspect, relative spacings in time between the PSS and SSS for thefirst carrier may be different from the relative spacings in timebetween the PSS and SSS for the second carrier. In an aspect, the firstcarrier may be a legacy carrier and the second carrier may belong to anew carrier type. In an aspect, the information may be received afterinitiation of an active call. In an alternative aspect, the informationmay be received at or during acquisition procedures. In an aspect, theinformation may be received in a neighbor list, for example, a unicastneighbor list or a broadcast neighbor list.

In an aspect, periodicity of the PSS and SSS for the first carrier issame as periodicity of the PSS and SSS for the second carrier.

In some cases, the information may include one or more bits. Forexample, the information may include at least one bit indicating whetherthe second carrier is a legacy carrier (recognizable by “legacy” UEs) ornew carrier (not recognizable by “legacy” UEs). In an aspect, theinformation may include at least one bit indicating that the secondcarrier is a carrier not supported by legacy UEs. The information mayalso include at least one bit indicating the duplexing mode, e.g., TDDor FDD. Alternatively, the duplexing mode may be implicitly indicated bythe band number or channel number of the carrier. Thus, it may not benecessary to maintain different relative positions of the PSS/SSSsignals in order to distinguish between FDD and TDD for the new carrier.In an aspect, the information may also include at least one bitindicating the cyclic prefix type of the second carrier.

In certain aspects, a relative spacing in time between PSS and SSS maybe different depending on whether a FDD mode or a TDD mode is used. Inan aspect, relative spacings in time between PSS and SSS for the firstcarrier may be different from the relative spacings in time between PSSand SSS for the second carrier.

In certain aspects, a relative spacing in time between PSS and SSS maybe the same regardless of whether the received information indicates aFDD mode or a TDD mode.

The operations 600 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 6. For example, operations 600 illustrated in FIG. 6may correspond to components 600A illustrated in FIG. 6A. In FIG. 6A,the transceiver 604A may receive a signal on a first carrier and thePSS/SSS detector 602A may detect a PSS and SSS for the first carrier.The transceiver 604A may thereafter receive information indicating asearch space for a PSS and SSS of a second carrier. The detector 606Amay then search for the PSS and SSS of the second carrier based on thereceived information.

FIG. 7 illustrates example operations 700, performed by a base station(BS), for transmitting PSS/SSS of a new carrier type in accordance withcertain aspects of the present disclosure.

Operations 700 may begin, at 702 by transmitting a PSS and SSS for afirst carrier. At 704, information may be transmitted to a UE indicatinga search space for a PSS and SSS of a second carrier. At 706, the PSSand the SSS of the second carrier may be transmitted based on thetransmitted information. In an aspect, relative spacings in time betweenthe PSS and SSS for the first carrier may be different from the relativespacings in time between the PSS and SSS for the second carrier. In anaspect, the first carrier may be a legacy carrier and the second carriermay belong to a new carrier type. In an aspect, the information may betransmitted after initiation of an active call. In an alternativeaspect, the information may be transmitted at or during acquisitionprocedures. In an aspect, the information may be transmitted in aneighbor list, for example, a unicast neighbor list or a broadcastneighbor list.

In an aspect, periodicity of the PSS and SSS for the first carrier issame as periodicity of the PSS and SSS for the second carrier.

In some cases, the information may include one or more bits. Forexample, the information may include at least one bit indicating whetherthe carrier is a legacy carrier (recognizable by “legacy” UEs) or newcarrier (not recognizable by “legacy” UEs). In an aspect, theinformation may include at least one bit indicating that the secondcarrier is a carrier not supported by legacy UEs. The information mayalso include at least one bit indicating the duplexing mode, e.g., TDDor FDD. Alternatively, the duplexing mode may be implicitly indicated bythe band number or channel number of the carrier. Thus, it may not benecessary to maintain different relative positions of the PSS/SSSsignals in order to distinguish between FDD and TDD for the new carrier.In an aspect, the information may also include at least one bitindicating the cyclic prefix type of the second carrier.

In certain aspects, a relative spacing in time between PSS and SSS maybe different depending on whether a FDD mode or a TDD mode is used. Inan aspect, relative spacings in time between PSS and SSS for the firstcarrier may be different from the relative spacings in time between PSSand SSS for the second carrier.

In certain aspects, a relative spacing in time between PSS and SSS maybe the same regardless of whether the received information indicates aFDD mode or a TDD mode.

In certain aspects, a UE typically looks for frequencies at a 100 kHzraster. Thus, if the PSS/SSS positions are moved such that theirfrequency locations do not fall on the 100 KHz raster, then the UEs maynot find it. Thus, in certain aspects, a new carrier type may be madeinvisible to the legacy UEs by moving the PSS/SSS in frequency relativeto the frequency raster, e.g. by placing the PSS/SSS center on afrequency that is offset relative to standard center frequencies by anoffset value (e.g., k*100 kHz+n*15 kHz, for some k and some n). Thevalue of n may be selected, for example, to multiply the carrier spacingvalue (15 kHz in the present example) to put a search space nearly inthe middle of 100 kHz center frequencies. For example, n=3 would resultin an offset of 45 kHz, which is near the 50 kHz midpoint betweenadjacent 100 kHz center frequencies.

The value of n may be known a-priori (e.g., set by a standard) orsignalled to a UE by an eNB.

FIG. 8 illustrates example operations 800, performed by a UE, fordetecting PSS/SSS of a new carrier type in accordance with certainaspects of the present disclosure.

Operations 800 may begin, at 802 by determining a frequency offsetvalue. At 804, locations for a PSS and SSS may be determined for acarrier based on the frequency offset value and spaced centerfrequencies. At 806, the PSS and SSS of the carrier may be searched atthe determined locations. In an aspect, the frequency offset value maybe greater than an anticipated frequency error of the UE. In an aspect,operations 800 may further include receiving information indicating thefrequency offset value. In an aspect, the frequency offset value mayinclude an integer value times a frequency bandwidth value. In anaspect, the carrier may include a carrier of the new carrier type thatmay not be supported by legacy UEs.

The operations 800 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 8. For example, operations 800 illustrated in FIG. 8may correspond to components 800A illustrated in FIG. 8A. In FIG. 8A, afrequency offset determiner 802A may determine a frequency offset value.A location determiner 804A may determine locations for detecting a PSSand SSS for a carrier based on the frequency offset value and spacedcenter frequencies. Thereafter, a PSS/SSS detector 806A may search forthe PSS and SSS of the carrier at the determined locations.

FIG. 9 illustrates example operations 900, performed by a base station(BS), for transmitting PSS/SSS of a new carrier type in accordance withcertain aspects of the present disclosure.

Operations 900 may begin, at 902, by determining a frequency offsetvalue. At 904, locations may be determined for transmitting a PSS andSSS for a carrier, for detection by a UE, based on the frequency offsetvalue and spaced center frequencies. At 906, the PSS and the SSS of thecarrier may be transmitted at one of the determined locations. In anaspect the frequency offset value may be greater than an anticipatedfrequency error of the UE. In an aspect, operations 900 may furtherinclude transmitting information indicating the frequency offset value.In an aspect, the frequency offset value may include an integer valuetimes a frequency bandwidth value. In an aspect, the carrier may includea carrier of the new carrier type that may not be supported by legacyUEs.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Forexample, means for transmitting or means for sending may comprise atransmitter, a modulator 354, and/or an antenna 352 of the UE 120depicted in FIG. 3 or a transmitter, a modulator 332, and/or an antenna334 of the eNB 110 shown in FIG. 3. Means for receiving may comprise areceiver, a demodulator 354, and/or an antenna 352 of the UE 120depicted in FIG. 3 or a receiver, a demodulator 332, and/or an antenna334 of the eNB 110 shown in FIG. 3. Means for processing, means fordetermining, means for sampling, and/or means for cancelling out maycomprise a processing system, which may include at least one processor,such as the transmit processor 320, the receive processor 338, or thecontroller/processor 340 of the eNB 110 or the receive processor 358,the transmit processor 364, or the controller/processor 380 of the UE120 illustrated in FIG. 3.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and/or write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein, but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communications by a userequipment (UE), comprising: determining a frequency offset value;determining locations for detecting a primary synchronization signal(PSS) and secondary synchronization signal (SSS) for a carrier based onthe frequency offset value and spaced center frequencies; and searchingfor the PSS and SSS of the carrier at the determined locations.
 2. Themethod of claim 1, wherein the frequency offset value is greater than ananticipated frequency error of the UE.
 3. The method of claim 1, furthercomprising receiving information indicating the frequency offset value.4. The method of claim 3, wherein the frequency offset value comprisesan integer value times a carrier spacing.
 5. The method of claim 1,wherein the carrier comprises a carrier that is not supported by certaintypes of UEs.
 6. The method of claim 5, wherein the certain types of UEscomprise legacy UEs.
 7. An apparatus for wireless communications by auser equipment (UE), comprising: means for determining a frequencyoffset value; means for determining locations for detecting a primarysynchronization signal (PSS) and secondary synchronization signal (SSS)for a carrier based on the frequency offset value and spaced centerfrequencies; and means for searching for the PSS and SSS of the carrierat the determined locations.
 8. The apparatus of claim 7, wherein thefrequency offset value is greater than an anticipated frequency error ofthe UE.
 9. The apparatus of claim 7, further comprising: means forreceiving information indicating the frequency offset value.
 10. Theapparatus of claim 9, wherein the frequency offset value comprises aninteger value times a carrier spacing.
 11. The apparatus of claim 7,wherein the carrier comprises a carrier that is not supported by certaintypes of UEs.
 12. The apparatus of claim 11, wherein the certain typesof UEs comprise legacy UEs.
 13. An apparatus for wireless communicationsby a user equipment (UE), comprising: at least one processor configuredto: determine a frequency offset value; determine locations fordetecting a primary synchronization signal (PSS) and secondarysynchronization signal (SSS) for a carrier based on the frequency offsetvalue and spaced center frequencies; and search for the PSS and SSS ofthe carrier at the determined locations; and a memory coupled to the atleast one processor.
 14. A non-transitory computer-readable mediumcomprising code for: determining a frequency offset value; determininglocations for detecting a primary synchronization signal (PSS) andsecondary synchronization signal (SSS) for a carrier based on thefrequency offset value and spaced center frequencies; and searching forthe PSS and SSS of the carrier at the determined locations.
 15. A methodfor wireless communications by a base station (BS), comprising:determining a frequency offset value; determining locations fortransmitting a primary synchronization signal (PSS) and secondarysynchronization signal (SSS) for a carrier, for detection by a userequipment (UE), based on the frequency offset value and spaced centerfrequencies; and transmitting the PSS and SSS of the carrier at one ofthe determined locations.
 16. The method of claim 15, wherein thefrequency offset value is greater than an anticipated frequency error ofthe UE.
 17. The method of claim 15, further comprising transmittinginformation indicating the frequency offset value.
 18. The method ofclaim 17, wherein the frequency offset value comprises an integer valuetimes a carrier spacing value.
 19. The method of claim 15, wherein thecarrier comprises a carrier that is not supported by certain types ofUEs.
 20. The method of claim 19, wherein the certain types of UEscomprise legacy UEs.
 21. An apparatus for wireless communications by abase station (BS), comprising: means for determining a frequency offsetvalue; means for determining locations for transmitting a primarysynchronization signal (PSS) and secondary synchronization signal (SSS)for a carrier, for detection by a user equipment (UE), based on thefrequency offset value and spaced center frequencies; and means fortransmitting the PSS and SSS of the carrier at one of the determinedlocations.
 22. The apparatus of claim 21, wherein the frequency offsetvalue is greater than an anticipated frequency error of the UE.
 23. Theapparatus of claim 21, further comprising: means for transmittinginformation indicating the frequency offset value.
 24. The apparatus ofclaim 23, wherein the frequency offset value comprises an integer valuetimes a carrier spacing value.
 25. The apparatus of claim 21, whereinthe carrier comprises a carrier that is not supported by certain typesof UEs.
 26. The apparatus of claim 25, wherein the certain types of UEscomprise legacy UEs.
 27. An apparatus for wireless communications by abase station (BS), comprising: at least one processor configured to:determine a frequency offset value; determine locations for transmittinga primary synchronization signal (PSS) and secondary synchronizationsignal (SSS) for a carrier, for detection by a user equipment (UE),based on the frequency offset value and spaced center frequencies; andtransmit the PSS and SSS of the carrier at one of the determinedlocations; and a memory coupled to the at least one processor.
 28. Anon-transitory computer-readable medium comprising code for: determininga frequency offset value; determining locations for transmitting aprimary synchronization signal (PSS) and secondary synchronizationsignal (SSS) for a carrier, for detection by a user equipment (UE),based on the frequency offset value and spaced center frequencies; andtransmitting the PSS and SSS of the carrier at one of the determinedlocations.